One pronoun, four jobs
Se laver means to wash oneself, but that is only one of four jobs the pronoun se can do. Which one applies also decides whether the participle agrees. The one to watch is the passive use: French speakers use it constantly, learners rarely.
The four values of se
1. Reflexive - to oneself
The subject acts on itself: Elle se regarde dans le miroir.
2. Reciprocal - each other
Several people act on one another: Ils se regardent en silence.
3. Passive - it gets done
The subject is a thing and undergoes the action: Ça se voit de loin.
4. Inherently pronominal
Verbs that do not exist without se: se souvenir, s'enfuir, s'en aller.
The passive use
The subject is a thing, the verb is in the third person, and there is no agent. English splits this territory three ways: a passive (it is eaten cold), an impersonal you (you don't say that), or an active that behaves like a passive (the book sells well). None of them is marked by a pronoun, so nothing in your English prompts you to reach for se. In French it is the natural choice for general statements about things.
How it sounds in real life
Ça ne se dit pas en français.
You don't say that in French.
Ce plat se mange froid.
This dish is eaten cold.
Ces chaussures se vendent très bien.
These shoes sell very well.
Ça ne se fait pas d'arriver les mains vides.
Turning up empty-handed just isn't done.
Reciprocal or reflexive?
In the plural the same sentence is often ambiguous, in French as in English: Ils se regardent can mean that each looks at himself (réfléchi) or that they look at each other (réciproque). Context usually settles it. If not, an addition helps.
Reflexive - each to himself
Made explicit with chacun, lui-même, eux-mêmes.
Ils se sont lavés chacun de son côté.
They each washed on their own.
Reciprocal - each other
Made explicit with l'un l'autre, les uns les autres, mutuellement, entre eux.
Ils s'aident les uns les autres.
They help each other.
Nous nous soutenons mutuellement.
We support one another.
Typically reciprocal verbs
Ils se sont rencontrés à Lyon.
They met in Lyon.
Nous nous écrivons toutes les semaines.
We write to each other every week.
Agreement of the participle
Pronominal verbs form the passé composé with être. Even so, the participle does not always agree with the subject: the rule for avoir is at work underneath. The participle agrees with a preceding direct object, and that is usually se itself.
When does the participle agree?
| Case | Agreement | Example |
|---|---|---|
| se = direct object | yes | Ils se sont rencontrés hier. |
| Inherently pronominal | yes, with the subject | Elle s'est souvenue de tout. |
| Passive use | yes, with the subject | Ces robes se sont bien vendues. |
| se = indirect object | no | Elles se sont téléphoné. |
| A direct object follows | no | Elle s'est lavé les mains. |
If the direct object does come before the verb, the participle agrees with it, even for a verb that would otherwise stay unchanged: elle s'est lavé les mains, but les mains qu'elle s'est lavées.
